We seek to address the problems of tolerance to peripheral tissue restricted self antigens. While the thymus appears to be the primary site for inducing tolerance to self, it is clearly not perfect in this function. Many tissue restricted antigens are not expressed by the thymus or bone marrow derived cells, and they are also not likely to be shed in sufficient quantities to be transported to the thymus by circulating macrophages or dendritic cells. It is important to determine how the immune system induces and maintains tolerance to such antigens, for immune responses to these antigens lead to devastating autoimmune syndromes such as insulin dependent diabetes and multiple sclerosis. With a detailed understanding of regulation of the immune responses to self antigens, it should be possible to develop methods of treatment to control immune responses in organ transplant recipients and patients with autoimmune disease. Our laboratory aims to study the issue of tolerance to self using transgenic mouse technology to develop precisely defined in vivo models. We have targeted the expression of foreign class II MHC transgenes to specific nonlymphoid tissues (pancreatic beta cells and pancreatic acinar cells) as model "self" antigens, and have discovered that tolerance to these peripheral antigens is indeed established, apparently by post-thymic mechanisms. Preliminary studies suggest that a major post-thymic mechanism for inducing tolerance in class II MHC reactive CD4+ T cells is the induction of clonal anergy/paralysis. Studies defined in this proposal seek to identify those factors that determine T cell susceptibility to clonal paralysis, and the physiological consequences of the induction of paralysis. This will be accomplished using detailed cell surface phenotype studies and functional analysis of paralyzed cells taken from the transgenic mice. The in vivo behavior of paralyzed cells will be studied in terms of their recirculation characteristics, lifespan, and ability to participate in immune responses. In addition, cells from normal nontransgenic mice will be studied to determine what subpopulations are most susceptible to paralysis, and whether a significant proportion of normal T cells are already paralyzed. Since class I MHC reactive CD8+T cells have many functional differences from CD4+ cells, we will study the mechanisms of tolerance in this subset as well by targeting expression of foreign class I transgenes to specific nonlymphoid tissues. Finally, we will determine whether our results can be incorporated into a new perspective on the mechanisms of immune regulation in vivo. The existence of significant numbers of paralyzed cells may have a major influence on the generation of immune responses. To test this, we will use adoptive transfer of populations of paralyzed cells specific for a known antigen to study their influence on immune responses by nontolerant cells to the same antigen.